Propeller



April 7, 1925.

I. L. ROBERTS PROPELLER Filed Oct. 15, 1918 2.Sheets-Sheet 1 A ril 7,1925.

' I. L. ROBERTS PROPELLER Filed on. 15, 1918 2 Sheets-Sheet 2 PatentedApr. 7, 1925.

ISAIAH I1. ROBERTS, OF

PATENT OFFICE.

uunva essence, ISLE or ruins, wnsr mums; Assrenoa on ONE-HALF T0 WILLIAMG. LIGHTENSTEIN, OF JERSEY CITY, NEW JERSEY.

. ZE'ROPELLER.

Application filed Getohcr 15, 1918." Serial No. 258,166.

To all 107mm it mag concern:

Be it known that I, ISAIAH L. Roennrs, av citizen of the United States,residing at Nueva Gerona, Isle of Pines, West Indies, have inventedcertain new and useful T111 provements in Propellers, of which thefollowing is a specification. 7

My invention relates to a new and useful propeller for use in propellingships or boats.

Heretofore all propellers known to me have blades which follow someuniform geometrical formula throughout their entire length and breadthas the screw or inclined plane. In order to get the highest efliciencyfrom this form of propeller the blades must be made thick near the huband comparatively thin in extension. H

If the blade is supported by a thick arm the support offers'a resistanceinstead of a help in operation. hen made wide enough to support theblade and thick enough to offer the minimum resistance to passingthrough the water it offers a large surface to the water when in motionand if the boat does not move forward in unison with the pitch of thepropeller the action of all that portion of the propellerblade moreorless distant from the hub then acts more or less as a churnor merelywhirls the water and thus is consuming power uselessly, It is difficultto keep adjusted thespeed of such propeller to the forward movement ofthe boat so that high efficiency may be attained and if attained .underfavorable engine power and clean boat surface these. conditions aredifficult to maintain constantly in practice. Hence in practice owing tochange of engine power and to fouling of hull or difference in speedowing to a light or heavy cargo which naturally varies the speed of theboat, propellers now made can notbe uniformly of equal efficiency inpractice.

What has been said above is not so true of that portion of the bladefrom the center or midway out to the end. This portion of a propeller isreally the working part and yields vastly more thrust or push to thevessel thanthe portion between the middle of the blade and the hub; somuch so that if the blade is made of a uniform width and pitch thethrust increasesv as the square of the distance from the center of thecircle described by said blade in turning. Further more, all bladedscrew propellers known to me have the widest part of their blades 7 andnear their centers and from thence taper moreor less to rounded points,thus losing or failing to secure propelling surface and supportingsurface against slip at the most useful and advantageous point in theentire blade.

In all propellers there is a further loss of power due to slipping.

My invention has for its object the design of a propeller which avoidsand overcomes to large extent the above'difliculties and increases theefiiciency orthrust of the propeller over a plain screw at all speeds ofthe boat or propeller.

In order to accomplish these results a radical departure has been madein the general design and construction of my propeller, a description ofwhich follows wherein like letters refer to like parts'in theaccompanying drawings in which:

Figure 1 is a plan view of a tar-med propeller;

Fig.2 is an elevation of Fig. 1;

Figs. 3, 4, 5' and 6 are sections on the planes AB, (I -D, EF, and G-'H,respectively indicated in Fig. l;

Fig. 7 is a plan view of a modified form;

Fig. 8 is an elevation of Fig. 7.

Referring to Fig. 1, the propeller is shown as consisting of fourblades, 1, 2, 3 and 4, connected by curved arms 5, 6, 7 and S to a hub9.

The arms 5, 6, 7 and 8 are not only formed on a curved axis, but theirrearward or thrust surfaces are concaved or formed as warped surfaces,whose chords are 'set on pitch lines co-ordinating with pitch lines ofthe helicoidal blades. These concave surfaces are so shaped'in orderthat they may act as propelling surfaces tending of themselves to act aspropellers as well as means for supporting the blades located at theirouter ends. The arms 5, 6, 7 and 8 are made with tapering trailingedges, the surfaces 14 being inclined to the concave surfaces, theelements of these surfaces being indicated at 10, 11, 12 and 13 in Figs.3 to 6.. The opposite or forward faces of :the arms are formed withsurfaces as indicated in Figs. 3 to 6, the eifect of this constructionbeing to facilitate the flow of water thereover.

The arms 5, 6, 7 and 8. as a whole are inclined to the longitudinalaxial plane of the hub 20, and made th'i'n at their advancing edges sonsto provide an easy entrance into the water, and the arms are axiallycurved into approsjmatcly semi-circular form, be cause the sharper thecurve the less resistaiice is offered in revolving in the water. By theconstruction of the arms in the man ner described I provide withrelatively small arms an adequate support for the blades which offer theleast resistance in turning P lat the same time obtain additionalpropellingetiect with a an'inimum or obstruction to the passage of thewater through the central portion of the propeller.

The concave arms 5, 6, 7, 8 terminate in blades 1, 2 3, r, rihose orkingsurfaces are circumferenti iy'e' tending portions of heiicoids, and boththe inherandouter edges of these blades extend'along helice having thesame pitch.

A. propeller inad'e in the form shown in the drawii'igs and describedabove yields a much higher eiiiciency than any other lcnown to me. Thearms yield aproportional return of thrust for the powcr appliedto themas do the terminal blades and have greater resistance to slip thanplain'arms'or'a helix. Their form and the ejecting ottheavater to the rear inlines directly opposed to the progress ofthe boat; causes an equalstraight thrust at all times.

The rear termination of the concavity of the arms pointing directlyrearward 'produces a greater "efficiency than can be "ob tained if theWater is ejected-at "any angle to the line traversed the boat inits-progress. The convexity 01" the opposite side to the concavityproduces a suction when the arm is rotating and-this'suctioh is in frontof the arms and in thedir'ection the boat is traveiing andmateriallyadds to the thrust. The curve'o'f said'arm 'in anarcofa'circle minimizes the resistance to the passageor rotary n'iovemeiitthereof throu 'gli'the Water. The concavity further gre'atly strengthensthe-arms and necessnates less metal in eonstruction. The angularprojections '-at'10, 11, l2, l3 rearward on the arms shownflad'dstrength to the arms andheing'tap'e'red to 'a sharp angle rearwardlytend 'to prevent "cavi ating at high speeds.

The blades in area greatly ex'ce'edtheir respective arms or support-s.Th'e'objectof making said vanes of'such is two-fold. The propellingforce of any pr'opeller is greatest at its greatest distance from thecenter of the hub, areaffor' area' thereof, c'ons 'h'n'ed;'also thequantity or area of crosssec ion of water out tlirough in revolving isgreatest and as the \v'ater' is theiibutm'ent against Which thepropeller gets its thrust it is ii'np'o'rtant to secure as large anabutment as possible. v

IIoexact rule canjhere be-"giveinfor the percentage of area oi 'theseblades toihc tage may however be varied for conditions of use. In thecase of towing, Where the speed *of the boat is slow and a strong pullis required blades of larger area may he used, While on high speed boatsblades of smaller area may be used to advantage. The greater the areathe less Willbe' the slip.

The high 'cfiiciency of v a propeller constructed asabove described isdue to several factors which include (1) the form and arrangement of thearms, whereby there is aiiorded easy passage'of thewater'through thecent a1 portion of the propeller, as the boat advances, with the lowestresistance to or disturbance of this central column of Water; '(2) the iac-tthat the arms though relatively small yetexert considerable thrustoperative; because of the form of the c0ncavity, 'to'forcethe' waterstraight back; 3) the relatively large area of blade surface located atthe greatest possible distance from the axis, whereby slip is lessenedto a high degree; and (4:) theexact curvatureiot the edgesofthe bladesto the curve of the spiral through which they travel 'in rotating,

This large area ofblade and "arm surface Working effectively againsttheWater, as an abutment, further obviates, to a large de 'gree, thenecessity for nice adjustment of thepitch-ofthe propeller blades tothelines or 'speed of the particular'vesselon which the p'ropell'er'isto be used, and the efficiency of the-propeller is maintained Within aWide range ofv'ariation of speed of travelof the boat or of variation inthe rate of rotation otthe propeller.

it "will be noted, furt-her; that'the major portion of the area of thepropellerislocated' at its'outer or peripheral part and preferablybeyond an imaginary cylindrical surface having a radius of about liveeighths that of the propeller as a Whole. The blades lie approximatelybetween two limiting cylindrical; surfaces or'in cylinders co-axi'alwith the' propeller. The diameter of the -propeller, as herein shown anddescribed is 1'6 inches and the pitch is'22' inches, which may howeverbe Ina'de greater or less a'cc0rding' to the speed at Which the boat isdesigned to go. r-is the rearWard concave Warped surfaces of thepropeller arms havethe same pitch as the Working blade surfaces andthese surfaces merge into each other, the propeller as a Whole closely"approaches the-ideal condition of a sc'rewivcrlizing into the water asinto-a solid nut. Th-isideaI c'on'ditio'n'is more closely approximatedbecause of the particular construction of the arm portions,

5 manner, but has the advantage that there is less liability of theblades catching in ropes or weeds.

In the form shown in Figs. 7 and 8, the arm-portions 5 6 7 8 are of thesame construction and arrangement as the arms 5, 6, 7 and 8; but theblades 1, 2, 3*, P are extended, as shown, to one side only of the arm,the area of the blades being however substantially the same as that ofthe blades shown in Fig. 1.

lVhile I have shown a e-bla-de propeller obviously any different numberof blades may be used as conditions of use may require. Nor is myinvention limited to strictly helicoidal surfaces for the workingsurfaces of the arms and the blades, as slight variations from this formmay be made without departure from the spirit of my invention.

1. A propeller comprising a plurality of ciflcumferentially and axiallyextending heliooidal blades and arms lying in substantially the sameradial plane connecting the blades to the shaft, said arms havingconcaved propelling surfaces Whose cords are set 1 on pitch linesco-ordinating with the pitch lines of the heliooidal blades.

2. Propeller according to claim 4; in which the arms are axially curved,their convex edges pointing in the direction-of rotation.

3. Propeller according to claim 4 in which the concave propellingsurface of each arm is defined by progressively varying radii ofcurvature, the radius being shortest adj acent the hub and longestadjacent the line of union with the blade.

In testimony whereof I afiix my signature.

ISAIAH L. ROBERTS.

